The invention relates to a residual current device, and in particular, to a ground leakage current circuit breaker (FI circuit breaker).
Residual current devices are used to ensure protection against a dangerous body current in an electrical system. Such a current occurs, for example, when someone touches a live part of an electrical system. The fault current (or differential current) then flows via that person to ground, as a body current. Protective devices, which are used for protection against dangerous body currents, safely and quickly isolate the relevant circuit from the main system when the so-called rated fault current is exceeded.
The design of residual current devices is known, for example, from xe2x80x9cetzxe2x80x9d (1986), Issue 20, pages 938 to 945. This illustrates, particularly in FIGS. 1 to 3, outline circuit diagrams and functional principles of a ground leakage current circuit breaker (FI circuit breaker) and a differential current circuit breaker (DI circuit breaker). Ground leakage current and differential current circuit breakers are constructed in a similar way from three assemblies. When a fault current occurs, a voltage signal is induced in the secondary winding of a core balance transformer through whose transformer core all the current-carrying conductors of a conductor network are passed. This signal actuates a tripping relay which is connected to the secondary winding via tripping circuit electronics. The tripping relay then operates a switching mechanism, by means of which the conductors of the conductor network are isolated. In this case, the ground leakage current circuit breaker is coupled to the conductor network exclusively and inductively via the core balance transformer. It thus takes the energy required for tripping from the fault current itself, independently of the main voltage. In contrast, in a differential current circuit breaker, tripping is carried out in a manner dependent on the main voltage, by means of an amplifier circuit with a direct electrical connection to the conductor network.
In order to avoid damage if used incorrectly, a residual current device must be protected against thermal overloading. This prevents the residual current device from failing if overloaded, or from itself becoming a source of danger as a consequence of thermal destruction. For example, the Austrian Installation Regulations xc3x96VE-EN 1, Part 1, Section 12.12 require overload protection for residual current devices. Since only residual current devices which are independent of the main voltage are approved for use in most of the European countries, in accordance with the Standard EN 61008, it is particularly desirable to have overload protection which can be combined with a residual current tripping circuit which is independent of the main voltage.
The invention relates to refining in a particularly advantageous manner a residual current device having overload protection and having a residual current tripping circuit which is independent of the main voltage.
A residual current tripping circuit which includes a core balance transformer and is independent of the main voltage, and has an overload protection. A tripping circuit is a circuit along which an electrical monitoring variable is produced, and this monitoring variable is assessed, and along which an electrical tripping signal is emitted to a tripping relay when a tripping condition is satisfied.
In one embodiment of the invention, there is a residual current device, including a residual current tripping circuit which is independent of the main voltage and includes a core balance transformer, an overload tripping circuit which is supplied with the main current, wherein the residual current tripping circuit and the overload tripping circuit include a common tripping relay for operating a switching mechanism which switches a conductor network, and a power supply unit connected upstream of the overload tripping circuit and connected via a respective supply line to each conductor of the conductor network, the power supply unit being designed with a high impedance such that each supply line has a resistance of at least about 2.5 kxcexa9/V-times the magnitude of the main voltage in volts.
In one aspect of the invention, the overload tripping circuit includes an evaluation circuit, which is connected to a temperature sensor and is upstream of a threshold value circuit, for determining a load state.
In another aspect of the invention, the temperature sensor is arranged in the region of the core balance transformer.
In still another aspect of the invention, the temperature sensor is a temperature-dependent non-reactive resistor.
In yet another aspect of the invention, the power supply unit includes a capacitor for storing the energy required to operate the tripping relay.
In another aspect of the invention, the overload tripping circuit is designed with a high impedance such that the current draw of the overload tripping circuit has an upper limit of about 80-90% of the quotient of 1/{square root over (3)}-times the main voltage and twice the resistance in each supply line where Ixe2x89xa6 and 0.8xe2x89xa6Fxe2x89xa60.9.
In yet another aspect of the invention, the power supply unit includes a capacitor for storing the energy required to operate the tripping relay.
In still another aspect of the invention, the overload tripping circuit is designed with a high impedance such that the current draw of the overload tripping circuit has an upper limit of about 80-90% of the quotient of 1/{square root over (3)}-times the mains voltage (U1/{square root over (3)}) and twice the resistance in each supply line where Ixe2x89xa6(F*U1/{square root over (3)})/(2*R) and 0.8xe2x89xa6Fxe2x89xa60.9.
According to this, the overload protection is arranged in an overload tripping circuit which is supplied with the main current. The residual current tripping circuit and the overload tripping circuit contain a common tripping relay, by means of which a switching mechanism which is arranged in the conductor network can be operated both by the residual current tripping circuit and by the overload tripping circuit.
A major advantage of the residual current device is that only the overload protection draws power from the conductor network. In contrast, the residual current tripping circuit is independent of the conductor network. The residual current device is therefore a ground leakage current circuit breaker which is independent of the mains voltage, in the sense of the Standard EN 61008. Since only one, common, tripping relay is provided for both tripping circuits, this results in a space-saving design and low costs.
The overload protection preferably has an upstream power supply unit, which is connected to each conductor of the conductor network in order to supply voltage. This ensures the operation of the overload protection even in the event of partial failure of the conductor network. Designing the power supply unit with a high impedance means that the overload tripping circuit is advantageously protected against high-voltage surges in the conductor network. In this case, each supply line including a resistance which is at least 2.5 kxcexa9/V-times the magnitude of the voltage, in volts, between any two given conductors of the conductor network. It is particularly advantageous to arrange the temperature sensor in the region of the core balance transformer, in particular in the immediate vicinity of those conductors of the conductor network which pass through the core balance transformer, where the thermal load on the residual current device is particularly high.
In one advantageous refinement, the overload tripping circuit includes a rectification circuit with a downstream capacitor. Owing to the high-impedance link between the overload tripping circuit and the conductor network, the power which can be drawn from the conductor network is not sufficient to trip the tripping relay. The energy required to operate the tripping relay is therefore stored by means of the capacitor within the overload tripping circuit. In order to achieve a particularly low current draw, the overload tripping circuit is designed with a high impedance such that the current draw in the overload tripping circuit satisfies the expression Ixe2x89xa6(0.8*U1/{square root over (3)})/(2*R). In this case, U1 is the mains voltage applied between any two given conductors of the conductor network, and R is the resistance connected in each supply line to the power supply unit. The factor F describes the ratio between the minimum voltage required for the equipment to operate and the lowest rated voltage. Typical values quoted in the Standards are, for example, 0.8; 0.85 or 0.9. In order to satisfy this condition, the components in the overload tripping circuit must have a correspondingly low current draw.
In one advantageous refinement, the overload tripping circuit includes a decoupling circuit which prevents the two tripping circuits from influencing one another. The decoupling circuit may be provided, for example, by a diode.